The scale of everything was a strict 1/4"=1' (O scale in model RR scales) and everything was taken directly from the engineering drawings. However, you have to realize that the castle was scaled down from 'reality', and the scale got smaller as it went up. If you are ever at WWoHP, you'll see what an effective visual trick it is.
The buildings were a combination of resin-cast brick, stone and shingles (so they could be done in sheets), and press board, basswood, and photo-etched brass for the windows. A little styrene here and there was used also. The snow was a modeling compound (can't recall the brand name now) like you'd find in craft stores; very similar to Crayola Magic Modeling compound.
The loco was a combination of styrene, expanded PVC sheet plastic, brass wire, laser-cut acrylic parts.
Mark